First of all, congratulations! This is a problem everyone here would like to have :)
As a true consultant, you must analyze the problem at hands using some structure, I think your short vs long term goals could be a way to do it:
1) Short-term goals;
- Financial opportunity: assuming you're going to enter at an entry-level the money will be similar, however, in my own experience, OW pays more.
- Work/Life Balance: On OW you tend to work on the client site from Monday through Thursday, with Fridays being spent in the office.
- Learning curve: pretty similar
- Traveling: OW is known for more traveling
2) Long-term goals.
- Moving inside the firm: path to partner is much faster in OW
- Exit opportunities: It will depend on what expertise you took during your years there but we can assume on OW you're going to focus more on the financial sector while on RB you're going to focus more on public sector
Obviously, the above analysis could be much more detailed but the overall key here is, on one hand, your objective ideas (what sector would you like to learn more about) vs your gut feeling (what people did you got a better vibe from, how did you felt there and so one)
Whatever decision you take it's going to be a wonderful experience!